A variety of methods involving the application of a motive force have been developed to remediate various types of soil and groundwater contamination of regulated materials. In the environmental remediation industry there is generally a lack of predictability in site remediation because subsurface soil and groundwater conditions are often heterogeneous and the delivery mechanisms for the motive forces are not efficient enough to overcome the heterogeneous conditions in a cost-effective manner. Current remediation processes are inefficient and somewhat ineffectual in some instances.
Most environmental cleanup activities are regulated by a government agency, such as a local, state, or federal environmental agency. A typical sequence of an environmental cleanup project involves several steps:    1. Assessing the environmental damage;    2. Establishing an initial pilot remediation protocol (approach, plan or technique);    3. Performing the pilot remediation according to the pilot protocol for a limited time or to a limited extent;    4. Monitoring the pilot remediation results;    5. Establishing a final remediation protocol based on the results of the pilot program;    6. Performing the final remediation over an extended period of time in a static manner (without changing or updating the protocol); and    7. Monitoring the impact of the final remediation over time to evaluate whether the final remediation needs be continued or is in fact completed.
These seven steps can be categorized in four major categories: assessment; pilot testing; remediation; and monitoring. Regulatory approval for implementing these phases of cleanup is generally required throughout the entire life of the project. The assessment phase (phase 1) consists of determining the rate and extent of contamination in soil, groundwater, and other media impacted by the release. In this phase, soil and groundwater is sampled and analyzed by a laboratory for constituents related to the released material. The released material can dissolve in water passing through soil and absorb to the soil above the water table or it can absorb to the soil above the water table in its natural state (free product). Similarly, groundwater within or beneath the location(s) of the release(s) can also contain dissolved and/or free product resulting from the release.
Drilling methods are utilized in this assessment phase to collect soil samples and to drill monitoring wells. Monitoring wells are used to sample groundwater and determine how far groundwater contamination has traveled in the groundwater. In addition, the groundwater elevations are determined to interpret the direction of groundwater flow. Additional hydrogeologic characteristics are determined in an attempt to predict the velocity of groundwater flow and to provide data to be used in the pilot testing and remediation phases of the project.
Following the assessment phase, enough information usually is known to select a remediation technique (protocol) that might be suitable for mitigating the damage. The remediation protocol often involves the application of a motive force to the subsurface of the ground (active remediation). Remediation can also involve physical removal of the contaminated media and disposal and/or treatment of the removed media above the subsurface (ex situ remediation). In the case of active, in situ remediation, the technique, protocol, or approach typically is tested via a small-scale pilot test that helps to determine the appropriate spacing between remediation wells and the appropriate sizing for the major remediation equipment to be utilized (sources of motive force). Monitoring occurs throughout the life of the remediation period and sometimes after the remediation is completed to ensure compliance with applicable cleanup standards. Monitoring generally consists of sampling soil and groundwater to demonstrate whether the soil and groundwater meet applicable regulatory requirements. Groundwater is generally collected from permanent monitoring wells.
These monitoring wells are installed by creating a hole (borehole) in the ground using a drill rig. A well is constructed within the borehole using a slotted well casing connected to a solid riser. A typical monitoring well construction consists of one screened interval that spans the water table in a desired vertical position to evaluate groundwater for the contaminants of concern. Sand is typically installed in the annular space (between the well casing and the wall of the borehole) to a depth slightly higher than the top of the slotted screen. The column of the sand in the annular space of the borehole is known as a sand pack. A seal is then used to prevent surface water or potential contaminants from entering the sand pack. The seal is generally constructed using bentonite, which is a cohesive clay material. The bentonite seal is installed above the sand pack. A grout consisting of a bentonite and cement mixture is used above the seal to further seal the top of the well.
Remediation wells are used to apply motive forces to remediate contaminated subsurface media. Remediation wells typically are constructed for the purpose of extracting gases or liquids from the subsurface or injecting gases or liquids into the subsurface. A network of remediation wells generally is used to impact the subsurface in a manner that reduces the contamination in the subsurface, as measured in monitoring wells that are sampled on a regular basis (usually quarterly or less frequently). An extraction well is constructed generally similarly to a monitoring well; however, the screen length is varied and the diameter of the wells and construction of the sand pack are varied in an attempt to improve the efficiency of removal of contaminated groundwater and vapors liberated from soil that has been influenced by the extraction. An injection well is generally constructed similar to a monitoring well except that the entire screen is submerged below the water table and the bentonite seal functions as a barrier to prevent injected materials from coming up the borehole, thereby allowing injected material to release more effectively to the subsurface. For injection of a gas, the top of the screen is generally installed below the contamination to allow the injected gases to transfer the contamination from a dissolved state to a gaseous state. Extraction wells may be used to recover the vapors from this process. Alternatively, injection of gases can be used to remediate contaminated soil above the water table. Liquid injection is generally used to allow chemical or biological processes to occur to remediate contaminated soil or groundwater. Until approximately 1995, these injection processes were generally implemented in open boreholes rather than in permanent remediation wells. Currently, the screened intervals for these injection processes are variable depending on the distribution of contaminated media that are targeted for remediation.
Prior to the installation of a permanent remediation well network and system, pilot testing is often conducted to assess the viability of a remediation protocol or technology(ies). During a pilot test, a remediation protocol (usually utilizing motive forces) is applied to a remediation well and observation wells are utilized to monitor the response of the applied motive force. The primary types of response usually measured during the pilot test are properties of the subsurface, influence (differential pressure) of the motive force on the observation wells, and the amount of mass contaminants removed. Traditionally, pilot tests are only performed one time in one part of a site. Therefore, effects of changing conditions can only be assumed or calculated based on currently available models. Also, heterogeneities in the subsurface make models far less predictable. A change in process that allows iterative and flexible techniques to be implemented throughout remediation is required.
Following completion of the pilot test, a design for the remediation well network and system is completed. The layout of the remediation wells and spacing between the wells is generally based on knowledge of the subsurface conditions and the response measured during the pilot phase. The criteria for spacing between wells and the design criteria for delivery of the motive force are based on research provided in the industry. The sources of motive forces are designed to deliver the appropriate amount of motive force to bring the contaminated soil and groundwater into compliance with appropriate regulatory standards. Upon completion of the design, plans are submitted to the environmental agency regulating the release. Upon approval by the regulating agency, the construction of the remediation system begins, including the installation of remediation wells, piping from the remediation well network to the location of the motive forces, and the fabrication of a motive force delivery system and controls for continuous operation of a system.
The remediation system may be designed to operate motive forces over the entire contaminated area at one time. Alternatively, manifolding of the piping can be completed so that motive forces can be applied to portions of the contaminated subsurface in a predetermined or programmable sequence. The construction sequence generally consists of the installation of the wells and associated piping first, followed by the fabrication of the motive force delivery system and controls, which is usually conducted off site. Upon completion of the construction process, the motive force delivery system and controls are delivered to the site and the system is started. Regular maintenance activities are conducted after the system startup.
One prevailing or widespread approach to the design of the remediation protocol is to try to accomplish the remediation with as few remediation wells, motive forces, and controls as possible in an attempt to minimize costs. To accomplish the remediation with very few wells it is generally regarded that the time required to complete the remediation of the site will be longer. The increased timeline results in higher operation and maintenance, sampling, and reporting costs. Also, once the remediation wells are installed there is not an easy way to modify the well network by adding more or different types of wells, if the data related to subsurface conditions and containment recovery warrant modifications.
The two most common broad types of motive forces for remediation are injection of liquids or gases into the subsurface and extraction of liquid or gases from the subsurface to cause reduction of contamination. The reduction of contamination may be obtained through mechanical, chemical, biological, and other processes that occur as a result of the injection or extraction motive forces. The delivery of the motive forces is often controlled with programmable logic controllers. The logic controller is generally programmed to adjust the motive forces based on conditions within the source of the motive delivery system, rather than based on conditions in the subsurface of the ground. For example, temperature sensors within the sources of the motive force may shut down the system when the operating temperature of the equipment becomes too high (e.g., to avoid damaging the motor). Other safety issues may be utilized including shutoffs when explosive conditions are present in the remediation compound area. Controls also are used to operate motive forces at different areas of the site in a preprogrammed sequence.
Currently, common indicators of remediation success are usually collected no more frequently than monthly or quarterly. Therefore, the need for significant operational changes are often identified over an extended period of time, adding to the remediation costs. Current industry practice does not use real-time data indicative of remediation success or failure in the programmable logic controller in a manner that results in effective, automatic system adjustments that maximize remediation efficiency or minimize undesirable effects of system operation. Also, there is not a method in the industry for easily changing motive forces to easily take advantage of the most appropriate motive force as the nature and extent of contamination changes or as subsurface conditions change throughout the life of an environmental remediation project.
Currently, prior art remediation often includes permanent wells at depths that span the contaminated areas and are used to monitor the influence that the motive force is having on the subsurface during soil and groundwater remediation. Currently, the wells typically are only capable of measuring influence at the wellhead, which does not provide an indication of where within the vertical column of the subsurface is being influenced by the motive force. It is only known that the influence is observed somewhere in the screened area of the well. The significance of not understanding vertically where the influence is being observed is that it is unknown whether or not the entire vertical column of contaminated subsurface is being treated. A process is needed to better monitor the success of remediation at varying vertical positions.
Much theoretical information has been published about the distribution of forces in the subsurface and the vertical profile of the groundwater surface that is influenced by applied motive forces. Generally, for a remediation well installed near the top of the groundwater surface typically the impact of the motive force is most prominent above the water table, because the soil above the water table contains air in void spaces, which is much less resistant than water. However, in a scenario where free product or contaminant dissolved constituents are present in groundwater, a larger vertical column requires influence below the groundwater surface to effectively remediate the release. During injection and extraction the entire vertical column of contaminated subsurface, particularly between remediation wells that apply the motive forces, is not always influenced by the particular motive force, making remediation of these areas incomplete or reliant upon natural remediation mechanisms of volatilization, biodegradation, advection, and other phenomena. Traditional remediation wells often only deliver motive force from/to one depth within the subsurface per location, thereby decreasing the likelihood of being able to influence a large vertical column of contaminated subsurface and decreasing the likelihood of intentionally influencing specific areas requiring remediation.
In a typical prior art remediation scenario, when a mechanical motive force is applied, contaminants are removed at a greater rate near the beginning of the application, and the removal rate decreases relatively quickly as an equilibrium condition occurs in the subsurface, thus a diminishing return is generally observed during the application of the motive force. Currently, the industry has utilized sequencing when applying motive forces, in other words, turning off motive force in portions of the remediation area or the entire remediation area. This method allows conditions to return to a static condition during the period of inactivity and in the short term it allows the ability to remove or treat a larger mass of contaminant when the motive force is reapplied. However, after repetition of the cycling of motive forces on and off, the mass removal reaches an equilibrium state faster with each cycle. The traditional explanation for this trend is that the overall mass of contaminant in the subsurface is decreasing thereby reducing the mass available for extraction. While this explanation is not totally unsound, a distinction must be made. The distinction is that the mass within the flowpaths of the applied motive forces is decreased and the mass available within the flowpaths is reduced. Therefore, a method of maximizing the mass removal of contaminants would be to change flowpaths when an equilibrium condition exists, thereby keeping subsurface flows in a dynamic state longer and allowing treatment of contaminants at varying horizontal and vertical locations within the contaminated areas. A method is needed to detect the equilibrium conditions and change the flowpaths by adjusting a given applied motive force or changing the type of motive force at varying horizontal and vertical positions to maximize contaminant removal.
Throughout the remediation process, undesirable effects can be created by the application of motive forces which can result in longer remediation time frames. Examples of undesirable effects would be creation of pore size preferential pathways, uncontrolled generation of vapors due to vapor injection, undesirable by-product generation due to chemical processes, and undesired movement of contaminated groundwater plume away from the source area. Current industry practice is to attempt to design for these undesirable effects prior to starting the system. However, the nature and extent of these undesirable effects cannot always be predicted and currently there is not a functional method for detecting some undesirable effects that develop after the system is started. A method is needed for detecting undesirable effects after system startup and correcting system operation without significant design changes.
There is currently not a method of easily changing technologies/motive forces at contaminated sites without having to make significant and costly changes to the remediation system components. For example, different technologies are needed at different times within a remediation project. Soil remediation techniques often involve a different motive force application than groundwater remediation. Also, free product in groundwater may be removed more efficiently and cost effectively via different technologies than dissolved contamination. Also, changes in subsurface conditions (chemical, physical, biological, or other) often necessitate that different techniques/technologies be applied. The result of changing technologies is that specific well designs, well spacing, piping, and major system components have to be changed, which can be cost prohibitive. A universal cost effective method is needed to allow for changing remediation technologies as conditions related to the nature and extent of contamination change.
In summary, the existing prior art for groundwater remediation does not allow for ease of monitoring data and controls that could enhance the ability to measure remediation effectiveness at the appropriate horizontal and vertical positions within the subsurface. Monitoring data and controls are needed that more adequately measure the effectiveness of the delivery of motive forces and adjust the motive force based on real time monitoring data to maximize remediation effectiveness and minimize undesirable effects. Further, utilization of a more efficient infrastructure that allow for ease in combining technologies and changing technologies can improve the overall remediation process.
The current methodology of the industry uses “brute force” without the use of any feedback from the operation of the remediation system as to how it is performing in effecting the clean up or even whether the selected system uses the appropriate technology. Accordingly, it can be seen that there is yet a need in the art for a method and apparatus for providing soil and groundwater remediation which takes advantage of performance information in order to utilize the appropriate techniques and resources at the appropriate time and to optimize the remediation being performed. It is to the provision of such a remediation method and apparatus that the present invention is primarily directed.